Spherical directional hydrophone with semispherical magnets



' Mfg? 26, 1969 P. F. HAYNER ETAL 3, 6 ,057

SPHERICAL DIRECTIONAL HYDROPHONE WITH SEMISPHERICAL MAGNETS Filed Oqt. 10, 1967 2 INVENTORS o I PAUL F. HAYNER a N N JIRAIR A. BABIKYAN BY MM 111,-

mum N nrromve'r 3,464,057 SPHERICAL DIRECTIONAL HYDROPHONE WITH SEMISPHERICAL MAGNETS Paul F. Hayner, Lexington, Mass., and Jirair A. Bablkyan, Providence, RI. assignors to Sanders Associates,

Inc., Nashua, N.H., a corporation of Delaware Filed Oct. 10, 1967, Ser. No. 674,238 Int. Cl. H04b 13/00 US. Cl. 340--8 20 Claims ABSTRACT OF THE DISCLOSURE A hydrophone, having a magnetic assembly and a spring-coil assembly movable relative to the fixed magnetic field provided by the magnetic assembly, which spring-coil assembly is driven by sound pressure. The magnetic assembly includes an improved magnetic member including a semispherical shell element forming a portion of the hydrophone housing. The magnetic member provides, within a given hydrophone volume, a maximized flux per unit volume.

SUMMARY OF 'INVENTION This invention relates to hydrophones, and more particularly, to a semispherical magnetic member adaptable for use on spherical directional hydrophones.

Conventional directional hydrophones using magnets of rod or ring configuration employ a housing which, by conforming in shape to the magnet configuration, enlarges the overall size of the hydrophone. A second shortcoming which also results in an increase in the size of the hydrophone and which is due to the characteristics of the magnets used, is the need for long magnet lengths for operation of those magnets at their maximum energy region. Thus, if such hydrophones are small they are inefiicient and if efiicient, they are large.

A further problem in the hydrophone art has been the elimination of noise, especially that noise generated by the drag of the hydrophone as it moves through the water or as water flows around a stationary hydrophone. When the hydrophone is of the rod or ring type, the noise varies as the flow direction changes because such types do not exhibit the same surface geometry in every direction.

Accordingly, it is a primary object of this invention to provide a hydrophone which efficiently provides maximum magnetic energy in a minimum volume and which has very low and uniform resistance to flow.

It is a further object of this invention to provide in such a hydrophone a magnetic member having a maximum of effective magnetic material, therefore maximum energy, in the smallest possible volume.

It is a further object of this invention to provide a spherical hydrophone having minimum flow resistance characteristics which are substantially constant regardless of the relative direction of the water flow and hydrophone movement.

It is a further object of this invention to provide a mushroom-shaped magnetic member which provides a maximum of effective magnetic material and maximum energy in the smallest volume and serves as a portion of the spherical housing of the hydrophone.

The invention is accomplished by a magnetic member having a semispherical shell element with an extension from the central portion of the inner surface of the shell element.

The magnetic member is adaptable for use in a hydrophone wherein the semispherical element forms a portion of the hydrophone housing, the hydrophone including a magnetic assembly which includes the magnetic member, and a spring-coil assembly movable in an air gap in the hired States Patent ice magnetic field provided by the magnetic assembly. The spring-coil assembly is driven by sound pressure.

DISCLOSURE OF SPECIFIC EMBODIMENT Other objects, features and advantages will appear from the following description of a preferred embodiment as shown in the attached drawings, in which:

FIGURE 1 is an exploded isometric view, with portions of individual parts removed, of a hydrophone according to this invention;

FIGURE 2 is a sectional view along a plane through the longitudinal axis of the hydrophone showing the magnetic paths; and

FIGURE 3 is a perspective view of the hydrophone of FIGURES 1 and 2.

There is shown in FIGURE 1 a hydrophone having a left-halfi assembly 10 comprising a mushroom-shaped magnetic member 12 which includes a semispherical shell 14 and cylindrical stem 15 which is preferably formed integrally with the central portion of shell 14. Bores 16, 18, 20, 22, 24 and 26, having their axes parallel to the axis of stem 15, are disposed in shell 14 about the perimeter of stem 15. Bore 28 extending through shell 14 and stem 15 receives a bolt 30 for fastening together the parts of the hydrophone.

A clamping ring 32 is positioned against the outer elements 36 of an S-spring 38 and a spacer 40 is positioned against the other side of S-spring 38. The three elements (32, 38, 40) are positioned against the ridge 56 of a ferromagnetic outer pole disc 52 and secured thereto by a plurality of fastening screws (not shown) forming a subassembly.

Three curved fingers 42, 44 and 46 suspend inner element 48 of spring 38 from outer element 36. A coil spacing ring 50 is cemented to the side of inner element 48 toward spacer 40.

The subassembly including clamping ring 32, S-spring 38, spacer 40 and outer pole disc 52 is so dimensioned that the outer perimeter 54 of ridge 56 of outer pole disc 52 fits snugly into the rim 34 of shell 14.

Right-half assembly 60 contains similar components, designated by primed numbers of their left-half assembly counterparts, and assembled in a similar manner; bores 16', 18', 20', 22', 24', and 26' in assembly 60 are not visible.

Central bore 62 in outer pole disc 52 receives a ferromagnetic inner pole disc 64, which is mounted between the ends of stems 15 and 15' and may be cemented to either or both of them. A central bore 66 in disc 64 receives bolt 30. The outer perimeter of disc 64 is suflicient- 1y less than the inner perimeter of bore 62 in disc 52 so that an annular air gap 68 is formed between them. Coil 70, having its edges 72 and 72' cemented to rings 50 and 50' respectively, is positioned in air gap 68 for axial movement relative to the outside diameter of inner pole disc 64, and the inside diameter 62 of outer pole 52.

When the hydrophone is assembled as shown in FIG- URE 2 shells 14 and 14' provide annular chambers 76 and 76' in a spherical configuration which functions as the hydrophone housing.

Because the hydrophone requires no additional housing a substantial excess volume is eliminated. And because the housing provided byshells 14, 14' is spherical the flow resistance is minimal and, more importantly, is uniform regardless of the direction of relative motion of the water and hydrophone so that noise caused by fluid flow around the hydrophone may be easily filtered out of the signal generated in coil 70.

A pair of magnetizing coil assemblies 80, 80', having leads protruding at 82, 82' from shells 14, 14', may be inserted within annular chambers 76 and 7 6' around stems 15, 15', respectively. The mganetizing coils may be potted and cemented to the walls of the chambers. After assembly, coils 80 and 80' may be energized to produce a strong magnetic field in their respective portions of the hydrophone. Then the coils may be deenergized and their leads 82, 82' clipped. The magnetic field created by coil assembly 80 extends, as indicated by arrows in FIGURE 2, through stem to disc 64, radially outward from 'disc 64 through air gap 68, coil 70 and disc 52, and then through shell 14 back to stem 15. The field created by coil 80' similarly extends through correspondingly numbered primed components. The magnets in these magnetic circuits may be made of Alnico-S and none of the components or cements in the magnetic circuit should be of a composition that would interfere with the efiiciency of the device.

The particular semispherical shape of shells 14 and 14' provides a maximum of magnetic material effective for conducting a confined magnetic field within a given hydrophone volume: the array of magnetic paths provided is not limited to one dimension or axis but is provided over a full three hundred and sixty degrees between the rim and the central portion of the shell.

In operation, with the assembled, magnetized hydrophone immersed in a fluid, the fluid completely surrounds the hydrophone and fills chambers 76 and 76'. When a sound or vibration occurs in the monitored area, the coinpression waves produced by the vibration are vented through bores 16, 18, 20, 22, 24, and 26 to chamber 76 varying the pressure therein. The hydrophone is directional, the output of coil 70 is a function of the cosine of the angle between its axis and the direction of the sound. Springs 38 and 38' act together and restrain the motion of coil 70 due to pressure variations. That is, coil 7 0 responds to pressure variations and springs 38 and 38 respond to coil motion by exerting restoring force. Tli'us coil 70 is driven to and fro in air gap 68 in response to sound pressure variation and as a result of its movement in the magnetic field in air gap 68, provides a signal which is a function of the cosine of the angle between the axis of the hydrophone which is the same as the axis of c'oil motion and the direction of motion of the sound source. Output leads from coil 70, not shown, may be connected to any suitable electronic apparatus, for signal analysis.

It should be appreciated that the semispherical shells and mushroom-shaped magnets may be used in apparatus other than a hydrophone, and that the specific embodiment described may be operative using only one mushroom-shaped magnet.

Other embodiments will occur to those skilled in the art and are within the following claims.

What is claimed is:

1. A spherical hydrophone comprising:

a spherical magnetic shell member having vent means,

means coupled to said magnetic shell member for forming a magnetic gap, and

means responsive to sound pressure for providing an electrical signal,

said means responsive being positioned within said magnetic gap.

2. The hydrophone of claim 1, in which said spherical magnetic shell includes two hemispherical members, and said means for forming a magnetic gap includes first and second magnetic cylindrical elements, one extending from a center portion of the inner surface of each said hemispherical members respectively toward the center of said spherical magnetic shell, a ferromagnetic inner disc coupled to said cylindrical element, and a ferromagnetic outer disc bisecting said spherical magnetic shell member and having a centralized aperture in which said inner disc is positioned.

3. The hydrophone of claim :1, in which said means responsive includes a coil assembly.

4. The hydrophone of claim 2, in which said cylindrical elements are formed integrally with said shell member.

5. A spherical hydrophone comprising:

a first hemispherical magnetic shell member,

a second hemispherical magnetic shell member,

a first magnetic member extending from the perimeter of said first hemispherical shell member,

a second magnetic member extending from the perimeter of said second hemispherical shell member,

a first ferromagnetic member connecting said first and second magnetic members,

a second ferromagnetic member connecting said first and second hemispherical shell members said second ferromagnetic member having an aperture therein in which said first ferromagnetic member is positioned,

first vent means extending through said first hemispherical shell member in the direction of the axis of said first magnetic member and adjacent to one end of said first ferromagnetic member,

second vent extending through said second hemispherical shell member in the direction of the axis of said second ferromagnetic member and adjacent to one end end of said second ferromagnetic member, and

means driven along the axis of said first and second ferromagnetic members in the space between said first and second ferromagnetic member by sound pressure and providing a signal that is a function of said sound pressure.

6. The hydrophone of claim 5, in which said first and second magnetic members are formed integrally with said first and second hemispherical shell members respectively.

7. The hydrophone of claim 5, in which said hemispherical magnetic shell members form the housing of the hydrophone for providing within a given hydrophone volume a maximized flux per unit volume.

8. The hydrophone of claim 5, in which said first and second magnetic members include a first and a second cylindrical element, each extending to the center of a spherical magnetic shell formed by said hemispherical members.

9. The hydrophone of claim 5, in which said first and second vent means each include a plurality of holes circularly arranged about the axis of said magnetic members.

10. The hydrophone of claim 5, in which said driven means includes a coil having externally accessible leads for sensing the current present in it.

11. The hydrophone of claim 10, in which said driven means further includes two resilient elements located on opposite sides of said second ferromagnetic member.

12. The hydrophone of claim 5 in which said shell members and said first and second magnetic members are permanently magnetiza-ble.

13. The hydrophone of claim 5 in which said shell members, and said first and second magnetic members are permanent magnets.

14. A hydrophone comprising:

a semispherical magnetic shell member,

a magnetic member extending from the central portion of the inner surface of said shell member,

a first ferromagnetic member coupled to the free end of said magnetic member,

a second ferromagnetic member having a central aperture for receiving said first ferromagnetic member surrounded by an air gap, said second ferromagnetic member extending radially outward to the rim of said shell member,

vent means, and

means movable in said air gap in the magnetic field provided by said members by sound pressure for pro viding a signal which is a function of the applied pressures.

15. The hydrophone of claim 14 in which said first magnetic member is a cylindrical element, and said second ferromagnetic member is a disc.

16. The hydrophone of claim 15 in which said movable means includes a coil movable in said air gap.

17. The hydrophone of claim 16 in which said movable means further includes a resilient element coupled to said coil.

18. In a hydrophone having a magnetic assembly, a coil movable in an air gap in the magnetic field provided by said assembly, the improvement comprising a magnetic member including a semispherical magnetic shell element forming a portion of the hydrophone housing, and'a second element extending from the central portion of the inner surface of said shell element, said member providing within a given hydrophone volume a maximized flux per unit volume. I

19. The hydrophone of claim 18 in which said second element is formed integrally with said semispherical shell element.

20. A mushroom shaped magnetic member adaptable for use in a hydrophone, comprising a permanent magnet semispherical shell providing a maximized flux per unit volume, the magnetic paths thereof extending between the center and the rim of said shell and a permanent magnet stem element extending from the central portion of the inner surface of said shell.

References Cited UNITED STATES PATENTS RODNEY D. BENNETT, JR., Primary Examiner BRIAN C. RIBANDO, Assistant Examiner 

